Conventionally, an image reading apparatus 101 which can read a transparent original is comprised of an apparatus main body 103 which includes an image reading device 102, and a transparent original irradiation apparatus 104 which is pivotally arranged on the apparatus main body 103, as shown in FIG. 8. The frame body of the transparent original irradiation apparatus 104 is formed by an upper cover 105 and a translucent lower cover 106 having a light diffusion effect, and it has a light source 107 for scan exposure, and a drive unit (not shown) for moving the light source 107.
When the image reading apparatus with the above arrangement reads image information of a transparent original F, the original F is set on a document glass table 108 of the apparatus main body 103. The light source 107 and image reading device 102 are synchronously moved and scanned in the direction of an arrow X in FIG. 8 while turning on the light source 107. In this way, light emitted by the light source 107 is guided to the image reading device 102 via the translucent lower cover 106 with the light diffusion effect and the transparent original F, thus reading the image information of the transparent original F.
However, when dirt such as dust exists on a transparent original F or the surface of the transparent original F is damaged (scratched), the conventional image reading apparatus reads even the dirt or scratch, so the image degrades owing to the dirt or scratch.
Recently, along with the development of a communication network and the increases in speed of a computer and capacity of a storage medium, the color image information is required to be treated at a higher resolution. In particular, when color image information is read by a scanner and the like, a demand for reading the image more accurately at higher speed and higher resolution has arisen.
When reading the image of the photographic film, a demand for reading the image information of the photographic film having a plurality of frames in a sleeve form more accurately at higher speed and higher resolution has arisen. As a means for reading a film at higher resolution, an image reading apparatus which has a means for removing the dust or scratch on the film is proposed. The Japanese Patent Laid-Open No. 2001-298593 is an example of the image reading apparatus. According to this proposal, the light source including the infrared LED for detecting the dust/scratch information and the light source for reading the image information is arranged as the surface light source, so that the image in which the influence of the dust or scratch is reduced can be read.
However, since the surface light source as an indirect illumination system has poor illumination efficiency, a device that synchronously moves an illumination system and optical system is known as a device that reads an image at higher speed and with higher image quality. As a method of controlling these illumination system and optical system, a method disclosed in Japanese Patent Laid-Open No. 10-004481 or the like is known. According to the technique described in this reference, the influences of, e.g., synchronous errors caused by positional deviation between the illumination system and optical system can be reduced as much as possible.
An example that relates to this reference will be briefly explained below using FIGS. 22, 23, and 24.
FIG. 22 shows an example of an image input apparatus which can read both a document original or the like, and a photographic film. FIG. 23 shows a state wherein the image reading apparatus shown in FIG. 22 mounts a fixing member used to fix a photographic film upon reading a photographic film.
A transparent original illumination apparatus 502 which is required for reading the transparent original such as the photographic film is arranged in an image reading apparatus 501, and electrically connected to the image reading apparatus 501 via a transparent original light source lighting inverter 507 and I/F cable 515 so as to be controllable from an image reading apparatus control board 503. The transparent original illumination apparatus 502 has a transparent original illumination unit 518 including a transparent original illumination unit 504 for reading the transparent original. An optical unit 514 includes a first reflecting mirror 509, second reflecting mirror 510, third reflecting mirror 511, and lens 512 which are required for optically forming the image of the transparent original on a CCD image sensor 513, and a reflecting original illumination light source 508 for irradiating the reflecting original such as the document original, and reads the image while scanning the original in the directions indicated by the arrows shown in FIG. 22 (in a subscanning direction) by the image input apparatus control board 503 and a motor 516.
The CCD image sensor 513 and image input apparatus control board 503 are electrically connected to each other via a signal cable 517. Hence, an electric signal photoelectrically converted by the CCD image sensor 513 can be obtained as image data by scanning the original while synchronizing the transparent original illumination unit 518 and optical unit 514 by the motor 516. A transparent plate 519 in the transparent original illumination apparatus 502, which exists between the transparent original illumination unit 518 and a film guide 505 on a document glass table 506 uses transparent glass or a diffusion member.
Upon reading a transparent original such as a film or the like, the film is fixed by the film guide 505 mounted on the document glass table 506. As shown in FIG. 23, the film guide 505 has a calibration region S used to calibrate illumination light coming from the transparent original light source 504. Also, A shown in FIG. 23 indicates one frame of a photographic film.
FIG. 24 shows an optical position alignment method required to synchronously scan the transparent original illumination unit 518 and optical unit 514.
The optical unit 514 is moved in advance to a position corresponding to the calibration region S formed on the film guide 505, which is set at a predetermined position, and the transparent original illumination unit 518 is scanned a distance D in the direction of an arrow before the beginning of image reading, so as to seek a position where an optical output becomes maximum or a position effective to read a film at nearly two end positions a and a′ within the calibration region S. Upon reading an image, a scan is made by maintaining that positional relationship all the time, thus allowing high-speed reading of a high-quality image.
However, for example, if the transparent original illumination unit 518 and optical unit 514 do not have a correct parallel positional relationship, the aforementioned method is effective for a case wherein the light amount distributions in the subscanning direction have broad uniform ranges, as shown in FIG. 25A. But when the light amount distributions in the subscanning direction have narrow uniform ranges, as shown in FIG. 25B, the aforementioned method cannot cope with since positions a and a′ have different maximum optical output positions.
That is, when the optical system and illumination system are laid out with a large tilt in the main scan direction, the light source must have a sufficiently uniform light amount distribution, resulting in a drop of illumination efficiency at the reading position. Or a precise layout is required so as not to generate a difference between the light amount distributions in the subscanning direction at positions a and a′ in the calibration region S, resulting in an increase in cost.
When a light source requires a warm up time like a cold cathode fluorescent lamp (to be abbreviated as a CCFL hereinafter), the illumination system and optical system can only be precisely aligned after the warm up time has elapsed. For this reason, a pre-processing time in an image reading process increases. Even when a plurality of frames are to be read or when intermittent reading frequently occurs due to communication problems, since the precision free from any positional deviation is required, a problem such as an increase in cost or the like remains unsolved.